Physical and biogeochemical processes controlling particle fluxes variability and carbon export in the Southern Adriatic

In the framework of the Vector Project downward particle fluxes have been measured in a station located in the centre of the South Adriatic Pit from November 2006 to August 2008.Sediment trap samples were collected at two different depths, below the photic layer (168 m) and near the bottom (1174 m), and analysed for total mass flux, for total and organic carbon, total nitrogen, carbonate, stable isotope of organic carbon (δ13Corg) and biogenic silica contents. The results have been integrated and compared with data obtained from previous research projects, carried out in the Southern Adriatic area in 1994–1995 and 1997–1998.Fluxes of particulate matter showed high seasonal and interannual variability, with maximum values in late winter–spring season. The organic carbon flux, followed the same seasonal trend, with higher values below the photic zone, and peaks in spring, related to blooms of silica and/or carbonates phytoplankton organisms (e.g., diatoms, coccolithophorids). The organic carbon export from the photic layer was of 5.2 and 2.1 g C m−2 y−1 reached the bottom.Climatological cycles and, in particular, the maximum depth of the convective vertical mixing determined the high fluxes measured in 1998 and in 2008 springs.Total mass fluxes measured at the bottom trap were twofold those measured below the photic layer, and showed a high lithogenic fraction, highlighting the presence of advective processes that appear particularly active in the area. These processes can be correlated with the spreading of dense waters coming from the north and central Adriatic, generally observed in spring. The elemental and isotopic composition of bottom trap samples, resulted similar to that of samples collected in the south-western Adriatic slope, corroborating the assumption that lateral advection other than vertical input were contributing to bottom particle fluxes.

► We determine the downward particle fluxes in the South Adriatic Pit. ► High seasonal and interannual variability of particle fluxes are observed. ► Silica and carbonates phytoplankton control the carbon export from the photic layer. ► High particle export is related to deep convection processes. ► Lateral advective contributions of particulate matter at the bottom are recognised.